  12 1
  
(((1 #0, 2 #0) #6, (3 #1, 4 #1) #7) #8, ((5 #2, 6 #2) #9, (7 #3, 8 #3) #10) #11, ((9 #4, 10 #4) #12, (11 #5, 12 #5) #13) #14) #15;